nyaml2nxdl converter: Some extra features

[RubelMozumder]

Feature List:

• [x] Preserving the nxdl file under the yaml file as comments, where there is a sha256 hash for yaml. So, when the nxdl file will be created from yaml file, the converter will create a new hash and compare it with the existing hash inside the yaml file.

• [x] Some nxdl attributes have unwanted '\n' char which breaks the XML

• [x] Collect 'copy-right' comment from yaml yaml fle if the comment is available there.

[RubelMozumder]

All points describe here in this issue are resolved.